Add updater.exe to FILES.cfg.

Bug: 926234
Change-Id: Ifcd0a9148f9488f57cde0e24acbcd46b3728eb20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1656348
Auto-Submit: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Michael Moss <mmoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668533}

chrome/tools/build/win/FILES.cfg

@@ -712,6 +712,12 @@ FILES = [
     'buildtype': ['dev', 'official'],
     'archive': 'chrome-win32-syms.zip',
   },
+  # Updater files (official build only):
+  {
+    'filename': 'updater.exe',
+    'buildtype': ['official'],
+    'archive': 'updater.exe',
+  },
   # Partner API files.
   {
     'filename': 'gcapi.h',